Car Alarms: alarm fault, horn siren, blown fuse

Question
i own a vauxhal cav sri 2.0 i ---the problem is i was adding a siren to the built in alarm -instead of having just a horn alarm--now when i set alarm off i get no sound from either horn ,siren even when connected seperately ---all i get is the indicaters flash only

Answer
Just a guess here, but it was 1 of 2 things
taht happened when you did that:
1 wrong polarity (likely).
Check all fuses in the car cabin, and under the bonnet.
The other choice is that the system needed a relay to
do this install, and you zapped it due to a high feed
horn and you added a low feed siren. No relay and pop
goes the circuit.  

This is a possibility, but remove the siren
from the wire it's on now, find the blown
fuse, replace, and try again. It sounds as if
the siren MUST use a relay if trying to use
the car's horn wire as your trigger output.
I would repair it, then skip this application
all together.

It's easier to put in an aftermarket alarm with a horn
output, along with a standard siren, then tying
to add an aftermarket siren to the factory alarm.
Can and obviously does in this case, cause damage.

Hopefully it's only a fuse.

Good hunting.

ALARMTEK